Careful. I've sent a quilt to my daughters Army unit to be signed, some of them grabbed sharpies, and they bled into the fabric. I heat set it all very well and warned the recepient of the fact that it may fade when washed (It was a home of the brave quilt, a young man in her unit was killed and the quilt went to his daughter)
I prefer the pigma pens, use a wider tip and have them write boldly and press. It may fade over time but at least they don't bleed.